1. Field of the Invention
The subject invention relates to pressure vessels for fluid storage, and more particularly to a metallic tank having a molded plastic liner, a thermal barrier for protecting the plastic liner during assembly of the vessel, and a connector for joining the metallic tank and plastic liner together.
2. Background of the Related Art
Pressure vessels that combine the strength of an exterior metallic tank and the passivity of an interior plastic liner are well known in the art. Such tanks have achieved widespread usage in the field of domestic fluid storage, including hot water storage tanks, hot water heating tanks and accumulators for hot water heating systems.
Because of the enclosed nature of these pressure vessels, they are more easily fabricated in several sections, which are subsequently welded together. However, great care must be taken when welding the tank sections together, to avoid damaging the interior plastic lining. Any damage or discontinuity in the lining could result in the eventual contamination of the contents of the tank and corrosion of the exterior metal components.
Several attempts have been made to overcome this problem. One solution has been to apply a liner coating to the metal tank after it has been welded together, as exemplified in U.S. Pat. No. 2,758,367. However, this limits the types of coatings that may be applied to the interior of a closed vessel. The process is also time consuming and expensive, and there is no assurance that the lining will completely cover the interior of the vessel as intended.
Another method of fabricating lined, multi-piece metallic vessels involves the use of a chill ring placed in the interior of the metallic vessel adjacent the weld area. The chill ring is usually an annular metal structure, which may or may not have a coating thereon. It serves to absorb the heat generated by the welding process such that it does not destroy the tank lining. The use of chill rings is disclosed in U.S. Pat. Nos. 2,412,271 and 2,970,719.
It is also known to utilize a rubber material as an insulating band installed adjacent to a welding area, as set forth in U.S. Pat. No. 2,587,840. However, the purpose of this insulating band is not to protect the lining of the tank, but to prevent the current generated by the electric welding process from jumping to an adjacent metallic wall.
Commonly assigned U.S. Pat. No. 4,241,843 discloses unique features to enable the welding of two metal tank sections together without causing damage to an interior plastic liner. In this instance two vertically divided foam insulation halves surround the interior plastic liner to form a heat shield around the liner and prevent damage thereto during the welding process.
U.S. Pat. No. 5,046,638 discloses a pressure vessel having an interior plastic liner, wherein a sacrificial fluoropolymer layer of material is provided adjacent the weld area, between the liner and the metallic tank, to protect the liner layer from the heat of weld formation.
Another problem associated with manufacturing a pressure vessel with an external metallic tank and a non-corrosive internal plastic liner is providing a cost efficient means for connecting the two structures together to form an integral vessel. The prior art is replete with connectors for this purpose. However, many are susceptible to leakage. Leakage at the connector can cause corrosion of the metallic components of the pressure vessel and can damage system components carrying fluid to and from the pressure vessel.
Clearly, there is a need in the art for a pressure vessel having an external metallic tank and in internal plastic liner that includes a insulated barrier for protecting the plastic liner from thermal damage during vessel assembly, and a leak-proof connector for joining the metallic tank and plastic liner together to form an integral vessel.